The overall goal of this research project is to describe the sequence of biochemical reactions which lead to the production of hydrochloric acid by the gastric mucosa and to identify the major control points in that sequence. The approach to this problem involves the use of non-destructive optical techniques for monitoring intracellular reactions together with more conventional analytical techniques. Currently, the project is specifically aimed at providing details of and testing a working hypothesis which generally includes the following sequence of events: 1) stimulation of secretion by conventional agents such as gastrin and histamine involves an increase in cellular cyclic-AMP; 2) cyclic-AMP produces a mobilization of specific substrates; 3) the specific substrates are metabolized via reactions which are directly linked to acid secretion, and; 4) the secretory process involves a redox-type mechanism which is coupled to the respiratory chain components.